(a) Technical Field
The present invention relates to a heat dissipation plate for a battery cell module. More particularly, the present invention relates to a heat dissipation plate, which can effectively dissipate heat accumulated in battery cells and a module, and a battery cell module having the same.
(b) Background Art
In an electric vehicle, a change or increase in temperature of a battery is often caused by heat generated within the battery due to high power output, high speed charging, and/or repeated charging. As a result, a thermal runaway phenomenon, which reduces the efficiency and stability of the battery, often occurs due to the batteries lack of ability to dissipate and transfer the heat to outside the battery rather than by the heat generated inside the battery.
For example, a lithium ion battery has an operating voltage of 3.6 V or higher and may be used as a power supply of a portable electronic device. Alternatively, a plurality of lithium ion batteries are connected in series and used as a power source of an environmentally-friendly vehicle such as a high power hybrid electric vehicle (HEV), a pure electric vehicle (EV), etc. Such a lithium ion battery has an operating voltage, which is three times higher than that of a nickel-cadmium battery or nickel-metal hybrid battery, and has a high energy density per unit of weight.
The lithium ion battery can be manufactured in various shapes. For example, a pouch-type battery cell, which has become widely used in the automotive industry, has a flexible case and thus can form into various shapes dependent upon its surroundings.
The pouch-type battery cell typically made of a flexible material that can be freely shaped and includes a battery portion and a pouch-type case having a space for accommodating a battery portion. The battery portion has a structure in which a positive electrode plate, a separator, and a negative electrode plate are stacked and wound in one direction. Alternatively the battery portion may also have a structure in which a plurality of positive electrode plates, separators, and negative electrode plates are stacked in multiple layers.
FIG. 1 is a schematic diagram showing a cell module 10 in which a plurality of pouch-type cells 11 are stacked. As shown in FIG. 1, adjacent cells 11 are connected to each other through an electrode portion 12, and it is necessary to provide a predetermined interval, e.g., 3 mm or more, between the adjacent cells 11.
This interval corresponds to a flow space 13 between the cells 11 through which cooling air is introduced and passed. When the cooling air passes through the flow space 13 between the cells 11, the heat of the cells is dissipated to the outside by the cooling air (the arrow of FIG. 1 indicates the flow direction of cooling air).
Changes in volume of the pouch-type battery cells are caused by intercalation and deintercalation of lithium ions in electrode materials during charge and discharge (See, for example, J. H. Lee et al., Journal of Power Sources 119-121 (2003) 833-837, the contents of which are hereby incorporated by reference). Damage to the separator due to expansion of the electrode plates in the battery cell causes an increase in voltage and a reduction in battery capacity as well as an increase in internal resistance, and thus an interfacial member for heat dissipation is required to respond to the expansion of the battery.
Furthermore, when the volume of the battery cell increases in a conventional battery system, the flow space formed between the cells is reduced to deteriorate the cooling performance, and thus the amount of heat generated between adjacent battery cells is increased due to an increase in temperature of the adjacent cells, resulting in a significant deterioration of battery performance. In addition, when the volume of the battery cells is significantly increased, a pouch case, especially those made of a polymer, may be damaged due to leakage of internal electrolytes and emissions of gas.
Additionally, a battery cell module and a pack are configured by stacking a plurality of pouch-type cells, and thus direct damage to adjacent cell may also occur when there is an increase in volume, gas leakage, or an explosion in any one of the cells.
Accordingly, in order to provide a compact heat dissipation system for the battery, which can improve the energy density with respect to the volume, the material should have excellent elasticity and heat dissipation performance to respond to the changes in volume.
The conventional battery case and housing are made of a material in which 20 to 30 wt % of mineral filler (e.g., a flame retardant material) is filled in a plastic substrate such as PC+ABS, PA, PP, etc. This material is flame retardant, chemically resistant, durable, etc., but has no heat dissipation properties.
Moreover, heat dissipation materials under development have focused on the increase in interfacial resistance through an increase in contact surface between fillers due to high density and the improvement of heat transfer characteristics. Furthermore, even plastic-based heat dissipation composite materials cannot effectively dissipate the heat generated from the pouch-type battery due to anisotropic thermal conductivity and low thermal conductivity.
In addition, in an air-cooled system of a conventional cell module 10 as shown in FIG. 1, it is necessary to provide a predetermined interval, e.g., 3 mm or more, between the adjacent cells 11, and thus it is difficult to improve the energy density with respect to the volume. That is, when the battery cell module 10 having a specific volume is configured, it is necessary to provide space between the cells 11, and thus it is difficult to increase the number of cells within the module. Moreover, when the number of cells is increased, the volume of the module 10 rapidly increases due to the space between the cells together with the thickness of each cell. Thus, there is an urgent need to develop a material optimized design for that is still capable of providing heat dissipation to the battery cell module while at the same time providing a more compact design.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.